BOM(Bill of Materials)是由Maven提供的功能,它通过定义一整套相互兼容的jar包版本集合,使用时只需要依赖该BOM文件,即可放心的使用需要的依赖jar包,且无需再指定版本号。BOM的维护方负责版本升级,并保证BOM中定义的jar包版本之间的兼容性。
使用BOM除了可以方便使用者在声明依赖的客户端时不需要指定版本号外,最主要的原因是可以解决依赖冲突,如考虑以下的依赖场景:
项目A依赖项目B 2.1和项目C 1.2版本: 项目B 2.1依赖项目D 1.1版本; 项目C 1.2依赖项目D 1.3版本;
在该例中,项目A对于项目D的依赖就会出现冲突,按照maven dependency mediation的规则,最后生效的可能是:项目A中会依赖到项目D1.1版本(就近原则,取决于路径和依赖的先后,和Maven版本有关系)。
在这种情况下,由于项目C依赖1.3版本的项目D,但是在运行时生效的确是1.1版本,所以在运行时很容易产生问题,如 NoSuchMethodError, ClassNotFoundException等。
BOM本质上是一个普通的POM文件,区别是对于使用方而言,生效的只有 <dependencyManagement>
这一个部分。只需要在 <dependencyManagement>
定义对外发布的客户端版本即可:
<?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.ydj.qd</groupId> <artifactId>inf-bom</artifactId> <version>1.0</version> <packaging>pom</packaging> <name>inf-bom</name> <description>第三方jar包统一管理</description> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding> <java.version>1.8</java.version> <spring.version>4.3.15.RELEASE</spring.version> </properties> <dependencyManagement> <dependencies> <!-- 阿里 --> <!-- https://mvnrepository.com/artifact/com.alibaba/druid --> <dependency> <groupId>com.alibaba</groupId> <artifactId>druid</artifactId> <version>1.1.12</version> </dependency> <!-- https://mvnrepository.com/artifact/com.aliyun.mns/aliyun-sdk-mns --> <dependency> <groupId>com.aliyun.mns</groupId> <artifactId>aliyun-sdk-mns</artifactId> <version>1.1.8</version> <classifier>jar-with-dependencies</classifier> </dependency> <dependency> <groupId>com.alibaba</groupId> <artifactId>fastjson</artifactId> <version>1.2.29</version> </dependency> <!-- Apache --> <dependency> <groupId>org.apache.commons</groupId> <artifactId>commons-lang3</artifactId> <version>3.3.2</version> </dependency> <dependency> <groupId>commons-collections</groupId> <artifactId>commons-collections</artifactId> <version>3.2.2</version> </dependency> <dependency> <groupId>org.apache.commons</groupId> <artifactId>commons-collections4</artifactId> <version>4.1</version> </dependency> <dependency> <groupId>commons-beanutils</groupId> <artifactId>commons-beanutils</artifactId> <version>1.9.1</version> </dependency> <!-- 谷歌 --> <!-- https://mvnrepository.com/artifact/com.google.guava/guava --> <dependency> <groupId>com.google.guava</groupId> <artifactId>guava</artifactId> <version>27.0.1-jre</version> </dependency> <dependency> <groupId>com.google.code.gson</groupId> <artifactId>gson</artifactId> <version>2.8.5</version> </dependency> <!-- 常用工具 --> <dependency> <groupId>joda-time</groupId> <artifactId>joda-time</artifactId> <version>2.7</version> </dependency> <dependency> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> <version>1.14.4</version> </dependency> </dependencies> </dependencyManagement> <build> </build> <distributionManagement> <repository> <id>maven-releases</id> <name>maven-releases</name> <url>http://mvn.ydj.com/repository/maven-releases/</url> </repository> <snapshotRepository> <id>maven-snapshots</id> <name>maven-snapshots</name> <url>http://mvn.ydj.com/repository/maven-snapshots/</url> </snapshotRepository> </distributionManagement> </project>
<dependencyManagement></dependencyManagement>
节点下首位处加入如下: <dependencyManagement> <dependencies> <dependency> <groupId>com.jlcx.qd</groupId> <artifactId>inf-bom</artifactId> <version>${version}</version> <type>pom</type> <scope>import</scope> </dependency> <dependency> ... </dependency> </dependencies> </dependencyManagement>
<dependencies></dependencies>
节点下引入如下: <dependencies> ... <dependency> <groupId>com.google.guava</groupId> <artifactId>guava</artifactId> </dependency> <dependency> <groupId>commons-collections</groupId> <artifactId>commons-collections</artifactId> </dependency> .... </dependencies>
如果需要使用不同于当前bom中所维护的jar包版本,则加上 <version>
覆盖即可,如:
<dependencies> ... <dependency> <groupId>com.google.guava</groupId> <artifactId>guava</artifactId> </dependency> <dependency> <groupId>commons-collections</groupId> <artifactId>commons-collections</artifactId> <version>3.2.1</version> </dependency> .... </dependencies>
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